AN EVALUATION OF A SURFACE-ENERGY BALANCE METHOD FOR PARTITIONING ET DATA INTO PLANT AND SOIL COMPONENTS FOR A SURFACE WITH PARTIAL CANOPY COVER

An objective, data-based method for partitioning evapotranspiration (ET) measurements into soil and plant components is tested at a cotton site against independently derived estimates of transpiration. This objective method requires standard meteorological/surface energy balance measurements and relies on a two-component (plant and soil) model for ET. Assuming that the soil surface humidity (or, alternatively, the soil evaporative resistance) and the soil Bowen ratio do not change much during any given day, their daily values are determined by a regression procedure which exploits the diurnal change in the meteorological data. Once the soil Bowen ratio is-determined, the available energy and ET data are partitioned into soil and plant components. Comparisons between the regression derived estimates of transpiration and transpiration estimates derived from sap flow gauges are made. An evaluation of the errors inherent in both estimates of transpiration is discussed.